1. Field of the Invention
The present invention relates to a golf ball, more particularly to a technology for improving resilience and shot feeling of a rubber composition used for a core of the golf ball.
2. Description of the Related Art
In a golf ball comprising a core consisting of at least one layer and a cover covering the core, the core is generally a molded body of a rubber composition containing a base rubber, a co-crosslinking agent and a crosslinking agent. The characteristics of a golf ball such as resilience and shot feeling are highly affected by the rubber composition constituting the core, and thus the improvement of the rubber composition has been under investigation. In order to improve resilience, a polybutadiene (so called high cis-polybutadiene) containing a high content of cis-1,4-bond is used for the rubber composition as the base rubber.
For example, Japanese patent publication No. 2002-282393A discloses a polybutadiene with 99% or more of cis-1,4-bond synthesized using a catalyst consisting of a composition which comprises a metallocene catalyst of a rare-earth metal compound, an ionic compound consisting of an uncoordinated anion and a cation, and/or aluminoxane. Additionally, Japanese patent publication No. 2002-338737A discloses a polybutadiene with 80% or more of cis-1,4-bond having a molecular weight distribution (Mw/Mn) of 1.2 to 2.0 synthesized using a catalyst consisting of a composition which comprises a metallocene catalyst of a rare-earth metal compound, an ionic compound consisting of an uncoordinated anion and a cation, and/or aluminoxane.
As described above, in a technology wherein the metallocene catalyst is used to enhance the rate of content of cis-1,4-bond, there exists a problem that it is unsuitable for industrial use since the metallocene catalyst is unstable in the air. Additionally, the polybutadiene has bonding types such as trans-1,4-bond and 1,2-vinyl bond other than cis-1,4-bond, and it is known that the reduction of the content of trans-1,4-bond enhances the resilience.